1. Field of the Invention
The present invention relates to transfer of signaling parameters, generated according to a prescribed source telephony protocol of a source network, to a destination via a transport network having a transport protocol distinct from the source and destination networks.
2. Description of the Related Art
Existing voice over IP protocols, for example session initiation protocol (SIP) and H.323, are limited in their respective abilities of transporting SS7 signaling information from a source network, for example a TDM based PSTN network, to a destination PSTN system via an Internet Protocol (IP) transport network. For example, an edge device serving as an interface between a TDM network and an IP network may filter certain parameters of ISDN User Part (ISUP) messages and transport a subset of ISUP parameters to a destination. Consequently, many features implemented in a conventional TDM based public switched telephone network cannot currently be performed within an IP domain.
For example, a decision about whether and how to route calls is restricted, based in part on an assumption in Internet Protocol that user terminals (e.g., call agents, access gateways, etc.) control whether and how calls are routed. However, many service providers having transport networks configured for providing transport services between networks may prefer to maintain control within their transport networks, and provide features based on control from nodes within their networks.
FIG. 1 is a diagram illustrating a prior art internetworking arrangement. The internetwork 10 includes a source network 12, a destination network 14, and transport networks 16a and 16b for transport of signaling and media connections between the source and destination networks 12 and 14. As illustrated in FIG. 1, the transport network 16a is configured as an IP packet network, and the transport network 16b is configured as an ATM packet network. The PSTN 12, implemented for example by a local exchange carrier, may implement ISUP protocol (“ISUP-X”) 20a using certain enhanced proprietary features for enhancing processing. The PSTN network 14 may be deployed as a network utilizing ISUP protocol (“ISUP-Y”) 20b having a different set of proprietary features relative to the ISUP protocol “ISUP-X” 20a of the PSTN network 12.
The IP packet network 16a, implemented for example using Session Initiation Protocol for Telephones (SIP-T) protocol, is configured for transporting signaling and media messages between the PSTN network 12 and the PSTN network 14 via transit services softswitches 18a and 18c. The SIP-T protocol is a peer to peer or proxy-able rendevous protocol where end devices, for example user agents (UAs), initiate multimedia or instant messaging sessions. The SIP-T protocol defines the signaling mechanism for multimedia calls and conferences, and uses several existing protocols established by the Internet Engineering Task Force (IETF) to provide message formatting, media negotiation (using Session Description Protocol (STP)), media transport (using Realtime Transport Protocol (RTP)), name resolution and name mobility support (using Dynamic Host Configuration Protocol (DHCP) and Domain Naming Service (DNS) queries), and application encoding (using Multipurpose Internet Mail Extension (MIME)).
The SIP-T protocol is an enhancement of the SIP protocol, in that SIP-T messages can carry existing ISUP or Q.SIG (a protocol used to for communications between private branch exchanges (PBXs) control messages as a payload. In particular, the SIP-T payload is defined as a MIME body part using the binary native encoding format. Hence, SIP-T can provide ISUP transparency over an IP network, so long as the end points 18 utilize the same SIP-T protocol, and so long as the source network and the destination network use the same version of ISUP. Hence, full ISUP transparency over an IP network 16a cannot be achieved without the networks 12, 14, and their respective gateways 18a and 18c utilizing the same ISUP protocol. In addition, the transport of proprietary ISUP parameters as SIP-T parameters still may result in loss of the proprietary ISUP parameters if the gateway 18 implementing the ISUP to SIP-T translation does not precisely map the proprietary ISUP into SIP-T parameters.
A fundamental problem with internetworking different telephony networks 12 and 14 via an IP network 16a is that multiple proprietary variations of ISUP protocol are implemented by service providers. Hence, encapsulation of proprietary ISUP features for transfer via an IP packet network 16a is only effective if the call agent 18c servicing the destination telephone network also services the same operator using the same proprietary ISUP protocol. However, if the call needs to be sent outside the customer's specific network, for example to another carrier or internationally, the proprietary ISUP features cannot be utilized due to the inability at the destination to recognize the proprietary ISUP protocol.
The ATM packet network 16b illustrates an alternate transport network used for internetwork communications. In particular, the ATM packet network 16b is configured for supporting Bearer Independent Call Control (BICC) protocol, established by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T). In particular, the ITU-T “Study Group 11” developed the BICC (ITU-T recommendation 1901) for introducing a fast packet switch infrastructure into a narrowband circuit switched network such as the PSTN networks 12, 14.
The BICC protocol, based on ISUP, is binary and highly structured, and is not native to the Internet domain. In addition, the BICC protocol favors continued use of limiting SS7 format characteristics, and may also result in multiple BICC variants as existing in ISUP.
Hence, there is a concern that a proprietary ISUP variant 20a, (e.g., ISUP-X) may not be recognizable by another ISUP variant 20b (e.g., ISUP-Y), resulting in loss of functionality as the calls are processed between the TDM networks 12 and 14.
Another concern is that the method of encapsulating ISUP information by a gateway 18 for tunneling via the IP packet network 16a prevents an intermediate node resident within the IP packet network 16a from being able to provide relevant services; for example, intermediate nodes forwarding the native packet may not be able to parse the packet in order to interpret the proprietary ISUP features encapsulated within the packets.